Ag表面对SF<sub>6</sub>初级分解产物氧化反应的影响作用研究

doi:10.19595/j.cnki.1000-6753.tces.230199

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Abstract Operational experience shows that the thermal stability of SF₆ in the gas-insulated equipment is lower than expected, and the metal surface inside the equipment may have a significant effect on SF₆ primary decomposition and secondary reactions, but the mechanism is not yet clear. First, it is necessary to study how the O₂ molecule dissociates and provides the reaction system with O atoms, which requires high energy; second, it needs to reveal the reasons for the significantly lower stability of SF₆ than expected in the actual fault state; third, it is necessary to investigate in depth the mechanism of the metal surface inside the GIS on the generation process of important characteristic products. Among the metal materials used in GIS, silver is usually plated on the internal contacts, electrical connections and other locations to lower the contact resistivity where the local over-thermal faults occasionally occur. In this case, the Ag surface is in direct contact with SF₆ gas and other impurity gases, while the mechanism of the interfacial interaction is not known and needs to be studied.
First, the adsorption configuration of O₂ on the Ag surface is obtained based on density functional theory, and the reaction model of low-fluorine sulfides with the O atom on Ag surface is established, which initially reveals the mechanism of oxidation reaction of SF₆ primary decomposition products on the Ag surface under GIS over-thermal fault state; Second, based on transition state theory and reaction kinetic theory, the energy barrier and reaction rate constant of interfacial reaction are calculated and compared with the corresponding gas-phase reaction, respectively. Last, the main reaction sites of the oxidation reaction paths of the three low-fluorine sulfides are identified separately, and the promotion/inhibitory mechanism of the reaction by the Ag interface is analyzed.
(1) The presence of the Ag interface enables the SOF₄ generation reaction, which is otherwise difficult to occur in the gas-phase space at both room temperature and superheated state, to proceed at room temperature, and its reaction rate is further enhanced with increasing temperature, which can be completed instantaneously with a low half-life of 5.05×10^-9 h at 400℃. Compared with the gas-phase reaction, the energy barrier of this reaction is reduced by 71.45% under the catalysis of the Ag surface. (2) The Ag surface also significantly reduces the activation energy required to generate SOF₃, allowing it to be generated rapidly at room temperature; the gas-phase formation reaction of SOF₃ is sensitive to temperature, which makes it have a faster reaction rate under over-thermal conditions. Both the Ag surface and the gas-phase space are important reaction sites for the formation of SOF₃. (3) Unlike SOF₄ and SOF₃, the Ag surface does not have a promotion effect on the generation of SOF₂. It raises the energy barrier of the reaction and significantly reduces the rate constant of the reaction. Accordingly, it is judged that SOF₂ is mainly generated through the direct reaction between SF₂ and O₂ in the gas phase space. The main reason may be the small molecular mass of SF₂ and the strong adsorption effect of Ag surface on it, which leads to the difficulty for the product to leave from the surface after SF₂ interacting with surface O atoms. Thus, the generation of SOF₂ gas molecules is inhibited.
The results of this paper reveal the mechanism of gas-solid reactions involving low-fluorine sulfides, oxygen-silver surfaces. The catalytic effect of Ag on several of these reactions is found, thus explaining previous doubts about the cause of SF₆ stability failure. The research methodology established in this paper is expected to be an inspiration in gas-solid reaction studies.

Key words： Gas insulated switchgear SF₆ thermal decomposition silver surface oxidation

Received: 21 February 2023

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	Li Haotian
	Zeng Fuping
	Yan Yiming
	Zhu Kexin
	Yao Qiang
	Tang Ju

Cite this article:

Li Haotian,Zeng Fuping,Yan Yiming等. Study on the Effect of Ag Surface on Oxidation of SF₆ Primary Decomposition Products[J]. Transactions of China Electrotechnical Society, 2024, 39(9): 2841-2850.

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https://dgjsxb.ces-transaction.com/EN/10.19595/j.cnki.1000-6753.tces.230199 OR https://dgjsxb.ces-transaction.com/EN/Y2024/V39/I9/2841

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